mediator (n.)

mid-14c., mediatour, "one who intervenes between two parties (especially to seek to effect a reconciliation)," from Late Latin mediator "one who mediates," agent noun from stem of mediare "to intervene, mediate," also "to be or divide in the middle," from Latin medius "middle" (from PIE root *medhyo- "middle"). Originally applied to Christ, who in Christian theology mediates between God and man. Meaning "one who intervenes between two disputing parties for the purpose of effecting reconciliation" is first attested late 14c. Feminine form mediatrix (originally of the Virgin Mary) from c. 1400. Related: Mediatorial; mediatory.